• Journal of Astronomy and Space Sciences
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• v.35 no.4
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• pp.219-225
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• 2018

Cosmic rays are ions that move at relativistic speeds. They generate secondary cosmic rays by successive collisions with atmospheric particles, and then, the secondary particles reach the ground. The secondary particles are mainly neutrons and muons, and the neutrons are observed by the ground neutron monitor. This study compared the diurnal variation in cosmic ray intensity obtained via harmonic analysis and that obtained through the pile-up method, which was examined in a previous study. In addition, we analyzed the maximum phase of the diurnal variation using four neutron monitors with a cutoff rigidity below approximately 6 GV, located at similar longitudes to the Oulu and Rome neutron monitors. Expanding the data of solar cycles 20-24, we examined the time of the maximum cosmic ray intensity, that is, the maximum phase regarding the solar cyclic modulation. During solar cycles 20-24, the maximum phase derived by harmonic analysis showed no significant difference with that derived by the pile-up method. Thus, the pile-up method, a relatively straightforward process to analyze diurnal variation, could replace the complex harmonic analysis. In addition, the maximum phase at six neutron monitors shows the 22-year cyclic variation very clearly. The maximum phase tends to appear earlier and increase the width of the variation in solar cycles as the cutoff rigidity increases.

• Journal of the Korean Statistical Society
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• v.30 no.1
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• pp.99-113
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• 2001

This paper deals with the problem of estimating the means in two inverse Gaussian populations with equal but unknown coefficient of variation. The maximum likelihood estimators are derived by solving a cubic equation and their asymptotic variances are presented for comparative purpose. Monte-Carlo simulation is conducted to investigate the efficiency of the estimators relative to the sample means over a wide range of values for the sample size and the coefficient of variation. The effect on this efficiency under the departure from the assumption of common coefficient of variation is also studied.

• Journal of Positioning, Navigation, and Timing
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• v.5 no.2
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• pp.87-96
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• 2016

The ionospheric error, which is one of many error elements considered during the Global Navigation Satellite System (GNSS) positioning, is hard to be predicted due to the influence of geomagnetic activity and irregular solar activities. Thus, the present study analyzed a change pattern in the ionosphere through Global Ionosphere Map (GIM) data for 12 years from 2003 to 2014 and a variation in the Slant Total Electron Content (STEC) between Sinuiju and Busan which was the longest range in the southeastern direction of the Korean Peninsula. The variation in the STEC verified the diurnal, annual, and solar cycle variations due to the influence of solar activity. The diurnal variation was characterized that the variation in the STEC started to increase from 6-7 am and reached the maximum at 13-14 pm followed by being decreased. The seasonal variation was characterized that the variation in the STEC was high in spring and autumn whereas it was low in summer and winter. The solar cycle variation revealed that the variation in the STEC increased during solar maximum and decreased during solar minimum. The variation in the STEC was up to 20 Total Electron Content Unit (TECU) during the solar minimum and up to 60 TECU during solar maximum.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.11
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• pp.3110-3114
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• 2009

Rotor temperature variation is a significant issue in the design of induction motor controls. In the literature, numerous studies have mentioned significant performance degradation due to rotor temperature variation unless it is taken into account. However, those studies have mainly focused on field-oriented control in terms of tracking performance. There was little research about the influence of rotor temperature variation on performance particularly in the case of optimal controls such as maximum torque per amp (MTPA) control strategy. This work investigates how to affect the performance of maximum torque per amp (MTPA) control strategy as rotor temperature varies in time. To this end, investigation was carried out in two ways to see whether the objective of MTPA control strategy is achieved regardless of rotor temperature variation. It is to produce a desired torque with the minimum possible stator current at the same time. Laboratory experiment shows that tracking performance and maximum torque per amp condition is significantly affected by rotor temperature variation as rotor temperature varies, thus ending up with performance degradation of MTPA control.

• Journal of Environmental Science International
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• v.9 no.5
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• pp.369-374
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• 2000

The estuary of Nakdong river is very influenced by the freshwater contained nutrients and organic materials. The response results of these influences are eutrophication and red tide outbreak in this region. Concentration of chlorophyll a was 0.78~62.55$\mu\textrm{g}$/L in February 1.20~21.29$\mu\textrm{g}$/L in April 1.88~188.35$\mu\textrm{g}$/L in June and 0.78~11.21$\mu\textrm{g}$/L in August respectively. The decrease of chlorophyll a is considered that residence time is shorten by increase of freshwater discharge and unfavorable growth condition of phytoplankton is created by diffusion of low salinity and increase of turbidity. The phytoplankton maximum region located inner side of this estuary during winter season whereas it was moved to outer side when mean discharge of the Nakdong risver was increased, Therefore the variation of phytoplankton maximum region was affected by input discharge from the Nakdong river basin.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2006.05a
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• pp.496-499
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• 2006

The solar cells should be operated at the maximum power point because its output characteristics are greatly fluctuate on the variations of insolation, temperature and loads. To obtain maximum power from solar cell, photovoltaic system cell power system usually requires maximum power point tracking controller. This paper propose Maximum power point tracking method using zero slope of differential value of maximum power. The power compare method traces to maximum power point rapidly but oscillate on the maximum power point largely, when quantity insolation variation is big. The power compare method is traces to maximum power point slowly but oscillate maximum point on the maximum power point smally, when quantity insolation variation is small. To solve two problem of the power compare method, designed zero slope of differential value of maximum power.

• Journal of Korean Society on Water Environment
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• v.27 no.6
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• pp.914-925
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• 2011

The variation of streamflow is regarded as one of the most influential factors on the fluctuation of water quality in the stream. The characteristics of the variation should be taken into account in the plans for the management of Total Maximum Daily Loads (TMDLs). This study analysed and characterized spatial distribution and temporal variation of streamflow at each unit watershed in Guem-river basin. For the analysis of the distribution of streamflow, the type and the extent of the distribution were investigated for the unit watershed. For the analysis of the variation, short and long term changes of streamflow were examined. The result showed that most of the distributions were not log-normalized and the extent of variation tends to be greater at the unit watershed placed on the tributaries in the basin. A kind of margin could be granted to the unit watershed involving high variations so as to establish the water quality goal and load allotment more reasonably and effectively in view of whole waterbody.

• Journal of Environmental Science International
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• v.9 no.5
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• pp.375-384
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• 2000

It is very important to interprete and simulate the variation of phytoplankton maximum region for the prediction and control of red tide. This study was composed of two parts first the hydrodynamic simulation such as residual current and salinity diffusion and second the ecological simulation such as phytoplankton distribution according to freshwater discharge and pollutant loads. Without the Nakdong river discharge residual current was stagnated in inner side of this estuary and surface distribution of salinity was over 25psu. On the contrary with summer mean discharge freshwater stretched very far outward and some waters flowed into Chinhae Bay through the Kadok channel and low salinity extended over coastal sea and salinity front occurred. From the result of contributed physical process to phytioplankton biomass the accumulation was occurred at the west part of this estuary and the Kadok channel with the Nakdong river discharge. When more increased input discharge the accumulation band was transported to outer side of this estuary. The frequently outbreak of red tide in this area is caused by accumulation of physical processes. The phytoplankton maximum region located inner side of this estuary without the Nakdong river discharge and with mean discharge of winter but it was moved to outer side when mean discharge of the Nakdong river was increased. The variation of input concentration from the land loads was not largely influenced on phytoplankton biomass and location of maximum region. When discharge was increased phytoplankton maximum region was transferred to inner side of the Kadok channel. ON the other hand when discharge was decreased phytoplankton maximum region was transferred to inner side of this estuary and chlorophyll a contents increased to over 20$\mu\textrm{g}$/L Therefore if any other conditions are favorable for growth of phytoplankton. decreas of discharge causes to increase of possibility of red tide outbreak.

• Journal of Preventive Medicine and Public Health
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• v.23 no.4 s.32
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• pp.451-464
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• 1990

The variation in resource utilization for hospitalized patients who had a group of similar diseases -- a Korean Diagnosis Related Group (KDRG) -- among the same type of hospitals was studied to assess the utillization variation due to the practice pattern of hospitals. Information about inpatients who were beneficiaries of the medical insurance for teachers and government officials discharged from 20 large university teaching hospitals in Seoul during 1986 and information about the hospitals were analyzed to achieve the study objective. A total of 20,223 non-outlier patients in 100 most frequent KDRGs were included in the analysis. Case charges after the review and length of stay (LOS) were used as measures of resource utilization during a hospitalization. A substantial variation among hospitals was found in most KDRGs : o the ratio of the maximum and the minimum among the mean case charges of hospitals was greater than 2 in 83 KDRGs ; o the difference between the maximum and the minimum among the mean case charges of hospitals was greater than 100,000 Won in 94 KDRGs : o the ratio of the maximum and the minimum among the mom LOS of hospitals was greater than 2 in 82 KDRGs ; o the difference between the maximum and the minimum among the mean LOS of hospitals was greater than 3 days in 94 KDRGs. The practice pattern of hospitals explained more than 20% of charge variation in 49 KDRGs and more than 20% of LOS variation in 43 KDRGs. The study results indicated need for a new health policy initiative for cost containment and quality assurance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.11
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• pp.2401-2408
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• 1997

The measured pulse shapes provided in the given data package demonstrated pulse distortions due to laser speckle. the distorted pulse shapes were carefully analyzed, modeled, and then applied to the DTTL(Digital-data Transition Tracking Loop)[1] bit synchronizer simulator to measure the mean time delay and its delay variation performance. The result showed that the maximum mean time delay variation with the modeled data was 12.5% when window size equals 1. All the data given were located within this modeled boundary and the maximum eman time delay variation was 7% in this case. The mean time delay variation was known to be smaller by reducing the window size [2][5][6]. The mitigated delay variation was 2.5% in the modeled case and 1.4% in the data set given when the windown size equals 0.1. With the digital DTTL insteal of analog DTTL, similar results was obtained.